Hydraulically operated tailstock



March 20, 1951 R. KURzwEn. ET Al.

HYDRAULICALLY OPERATED TAILsTocK 3 Sheets-Sheet 1 Filed July l0, 1948 N .mi

March 20, 1951 R. KURZWEII. ET AL 2,545,852

HYDRAULICALLY OPERATED TAILsTocK Filed July 10, 1948 3 Sheets-Sheet 2 fzag. 5

www@ 1 March 20, 1951 R. KURzwElL Er AL 42,545,852

- HYDRAULICALLY OPERATED TAILsTocK Filer; July 1o, 194e I s sheets-sheet 5 Patented Mar. '20, l1951 i UNITED STATES l PATENT 0FFlClf-Zk '2,545,852- HYDRALICLLY eremiti) mistook Robert Kurzweil,A VKew Gardens,-

Juveritiilo Pesqueira, Astoria, N. Y.; as'sig'nors to Morey Machinery Co.V Inc.,I Astoria,` N. Y.- v Application July 1o, 194s, serial' No. 'as

1o claims. (ci 812-31) The present invention relates to lathes and more particularly to lathe tailstocks';

It is an object of the present invention to pro-A vide a lathe tailstock with means adapted to slide the tailstock center and quill in axial direction.

It is another object of the present invention to provide in a tailstock means for sliding the tailstock center andl quill towards the workpiece, and to hold" it in operative position. x

It is a further object of the' present invention tov provide hydraulic means for operating theA center and quill sliding means' and for actuating the blocking means holding these parts" in operative position. F Y h Y With the above objects'V in View, the present invention mainly consists' of aYY lathe t'ailstock comprisi'ng in combination the following principle elements:

(a) A tailstock body;

(11) A quill arrangement mounted withinsaid tailstock' body rotatably and slidably in axial di"- rection thereof;

(c) AV tailstock center mounted within said quill arrangement slidably inaxial directionI of said tailstock body relativev tos'a-idquill arrange-l ment; .d

('diS'pring meanspermanently forcingvv said tailstock center outward into operative' position adapted toengage one end of a work piece; l

(el Blocking meansE on said` quill' arrangement preventing sliding of said tailstock" center in' outward direction beyond r said operative position;

(-f)'- Gripping means on said quill arrangement for' grippingly engagingV said endV of said work piece around said tail'stocliV center;

(g')` I-IydraulicA operating mea-ns for sliding said' quill arrangement together with said tail'stock center in axiat difreci'iionl of said tailstock body relative thereto;

(hij First actuating means for actuating said hydraulic operating rneans'sov that the same slides' said quill arrangement in axial-direction off said taril'stoclr` body towards said e'nd of said work piece; and- (i) Second actuating rneansfcrV actuating said: hydraulic means so that the same slides said quillv arrangementi'n axial directiono`i`" said tailstock body away from sai'dendf offsaid-'w'ork piece.

17naccordance with a-pref'erred embodiment' of the present invention. the quillv arrangement described above includes a l cylindrical supportmounted withinv thetailstock body; non-rotatably, but slidably in axial direction thereof, and a quill? mounted wiltlfi'i-'nl thisl cylindrical support at 2 the front end thereof rotatably relative to this support, but non-slidably in axial direction thereof.

The hydraulic operating means mentioned above' for sliding the cylindrical support, the quill and the tailstocli centerY include preferably a cylindricalbore within the rear part of the cylindrical supportextending ifi-'axial' direction thereof; a stationary piston within said cylindrical bore; a stationary piston rod arranged behindl said stationary piston secured at its iront end to said stationary' piston and at its rear end' to said' tails'tock body extending in axial direction of said cylindrical support; hydraulic actuating means for sliding's'aid cylindrical support together with said quill and ls'aid tailstock center in axial direction ofvsaid tails'tock body relative thereto; and" hydraulic conduits passing through said stationary piston rod and connecting said hydraulic actuating meanswi'th the two cylinder' compartments formed by said' stationary piston Within said cylindricaflbore in saidcylindrical support.

Furthermore, also in accordance with the presentinvention lo'cking-means are provided for holding the cylindrical support in operative position; thesev lockingm'eans' are operated by additional hydraulic means operatively connected with the hydraulic rnea'nsV for sliding the cylindrical support as explained above.

The novelfeatureswhich we consider characteristic for' the present invention are" set forth in particular in the appended claims. The invention itself',-y however', both as' to' its@ construction and its method of operation, together with additionalobjects' andadvantages thereof, will Vbe best' understood from` the following description of spe'cic embodiments when rea'dl' in connection with the accompanying drawings, in which:

Fig. 1 isa front elevational viewv of a lathe embodying the present invention;

Fig` 2 isa cross sectional kView of the lathe tailstock for-ming part ofl the lathe shown in Fig- 1,', taken on line 2-2o f Fig.' il; v u

Fig.* 3 is a cross sectional view of-V the lathe head'stock forming partof the lathe shown in Fig. l,` taken on line 5 3? of Fig. 1`;

lisa cross,v sectionv throughthe lathe tailsto'c'k shown Fig'. 2, taken on une' 4"-'4 of Fig. 2; and

Fig. 5 isa schematic Yshowing of they hydraulic means; for operating the variousV parts' of' the headstock andthetaustock n,

Referring now` in` detail to the" drawings,"v f designates a lathe" embodying the present'in" tion. This lathe serves for turning a work piece, for instance a railroad axle or the like.

This lathe I8 is composed of a base I2, a headstock I3 and a tailstock I4.

The headstock I3 comprises, as clearly shown in Fig. 3, a headstock body I5 on which is mounted a hollow headstock spindle I6 supported by the roller bearing Il and the front roller bearing I8. The roller bearing I1 is arranged in the rear wall I9 of the headstock body, whereas the roller bearing I8 is arranged in the front wall 29 thereof.

Fixed to the spindle I6 is a gear 2I meshing with the driving gear 22 This driving gear 22 is mounted on shaft 23. On this shaft 23, the gear 24 is mounted which engages gear 25 mounted on shaft 26. This shaft 26 is driven in any suitable manner, e. g. by means of a drive belt 2'I.

The spindle I6 is formed at its front end with an annular outwardly extending flange 28. In front of this annular ange 28, the nose 29 is arranged. This nose 29 is also provided with a ange 39 which is superimposed upon the front face of the annular flange 28 and secured to the same by means of screws 3 I. To the front face 32 of the nose 29, the annular ram ring 33 is secured by means of a plurality of screws not shown in the drawings.

This ram ring 33 is provided with a rearwardly projecting sleeve-shaped extensionr34 reaching into the bore 35 of the tubular headstock spindle I6.

In the front face 35 of the ram ring 33 a plurality of holes 3l are provided. In each of these holes, a spur 38 is inserted: These spurs 38 are provided with gripping edges 39 and adapted to drivingly engage the work piece I I when the same is in operative position.

In accordance with the present invention, a headstock center 49 is slidably supported by the sleeve-shaped extension 34 of the ram ring 33. This center 49 is provided at its front end in the usual manner with a conical piece 4I fitting into a corresponding centering hole on the work piece.

At its rear end, the center 49 is connected with the draw rod 42 by means of the screw 43. This draw rod is arranged slidably within the bore 35. Its turning within the tubular spindle I6, is however, prevented by means of key 43 secured to the inner surface of the tubular spindle I5 projecting into the bore 35 and the corresponding key way 44 provided in the draw rod 42, as clearly shown in Fig. 3.

The combined thrust bearing 45 is secured by means of screw 46 to the rear end of the draw rod 42. This thrust bearing 45 is connected also to the piston rod 47 of the hydraulic piston 48 arranged within the hydraulic cylinder 49; this hydraulic cylinder 49 is secured, as clearly shown, by means of screw 50 to the rear wall I9 of the headstock body I5.

The hydraulic cylinder 49 is furthermore connected by the ports 5I and 52 with the conduits 53 and 54, respectively. These conduits 5I and 52 connect the cylinder with hydraulic operating means for admitting hydraulic fluid into the cylinder 49; this hydraulic fluid moves the piston 48 within the cylinder 49, as will be described farther below in detail.

The tailstock I4 mounted on the base I9 includes a tailstock body 55 provided with a cylindrical bore 56. Within this cylindrical bore 56 the tubular cylinder 57 is slidably arranged. This tubular cylinder 5l is subdividedtby the partition 4 wall 58 into a front compartment 59 and a -rear compartment 69.

Within the front compartment 59 of cylinder 5I the quill 6I is freely rotatably supported by means of the roller bearings 92 and 63. This quill is non-slidable relative to the cylinder 51 but can be moved together with the same in axial direction of the tailstock body 55. The quill 6I is provided with the cylindrical bore 64; in this bore, the tailstock center 65 is arranged. This center 55 is permanently forced by spring 66 towards the work piece II so as to engage the center hole 9'! provided in the same. On the front face of quill 6I, the gripping projections 68 are provided. These gripping projections 68 are secured to the quill by means of screws S9.

In order to prevent sliding of the tubular cylinder 57 supporting the quill 9| in rearward direction while in operative position, i. e. while supporting the Work piece, a lock of the type shown in Fig. 4 is provided. This lock consists of two cylindrical locking members 'I9 and 'II arranged in a cylindrical bore 'I2 within the tailstock body 55. These cylindrical locking members 'I9 and 'II are provided with locking faces 'I3 and 74, respectively. These locking faces i3 and I4 are arranged so as to rmly engage the outer surface of the tubular cylinder 51 when the cylindrical locking members 'I9 and 'II are moved in direction of arrows 'I5 and 16, respectively. In this engaging position of the cylindrical members, movement of the tubular cylinder 5T and quill 6I in axial direction is completely blocked.

In order to enable sliding of the two cylindrical locking members 79 and 'I Il in direction of arrows 'I5 and '18, respectively, the cylindrical bore 'I2 is closed at its ends by closure plates I'I and 18, and hydraulic conduits 79, 89 and 8| leading to the ports 82 and 83, respectively, are provided for admission of hydraulic pressure iluid. Such pressure fluid is introduced through the inlet conduit 84 and operates the lock as will be described farther below in detail. v

It should be noted that the spring 85 arranged between the inner faces 88 and 81 of the cylindrical locking members 19 and 1I, respectively, permanently forces these cylindrical locking members 'III and TI apart from each other against direction of arrows 'I5 and 16.

The rear compartment 80 of cylinder 51 is closed at its end by the cap 88. This cap 88 is provided with a bore 89 through which the stationary piston rod 99 passes. This stationary piston rod 99 is secured at its rear end to the rear wall 9I of the tailstock body 55 and carries at its front end a stationary piston 92. Within this piston rod 198, the two conduits 93 and 94 are arranged; they connect the ports 95 and 95 with the space 9T behind the stationary piston 92 and the space 98 in front of the piston 92, respectively.

During chucking and removal of the work piece from the lathe, the above described arrangement operates as follows:

During chucking, the work piece, e. g. railroad axle II, is lifted by separate lifting means, not shown in the drawings, between the headstock I3 and the tailstock I4 with its centering holes properly aligned between the head stock center 4I and the tailstock center 95.

When the work piece II is in this position, pressure uid is admited by the four-way distributing valve 99 through the port 5I into the hydraulic cylinder 49 on the headstock I3, forcing the piston 48 together with the draw rod 42 and center 4I towards the work piece. This will iesultin engagement of the-headstock center 4| andv the corresponding center hole of the work piece II, and center 4| will slide the work piecewhile supported by the above mentioned lifting means-.towards the tailstock I4 into contact v with the tailstock center 65 and the griping projections 68 of the retracted quill 6I.

At this moment, pressure fluid is admitted by` means of the distributing valve and port 96 into the conduit 94 and through the same into the space 88 in front of the stationary piston 82, forcing the freely slidable cylinder 51 together with the quill 6| and the spring pressed center 65 in direction of arrow IUI. During the movement, the spring presed center 65 will engage the corresponding center hole 61 of the Work piece,

` neet the conduit 52 with a pressure line, thereby properly centering the same, and the gripping projections 88 will force the work piece against action of the hydraulic means provided in the headstock I3 in direction of arrow |0| towards the headstock.

We wish to note that this action is possible not due to a difference in line pressure within the various hydraulic conduits but due to the difference in the pressure faces of the pistons 92 and 48. Due to the fact that the pressure face of piston 82 is substantially larger than the pressure face of piston 48, the actual total pressure exerted by quill 6I will be ysubstantially larger than the pressure exerted by center 4I, and, therefore, it will be possible for quill 6I to move the work piece against actionrof piston 48 in direction of arrowv IOI. This movement will continue until the work piece engages the gripping edges 3e of the spurs 38, firmly pressed against the same.

During this period, the pressure of the pressure iluid admitted through the common conduit |02 to the port 95 for moving cylinder 51 through the conduit, 19 to the .port 82 of the locking mechanism'shown in Fig. 4 will be insumcient to operate the locking mechanism, i. e. to slide the locking cylinders 1|] and 1I against action of spring 85. However, the moment the cylinder 51 reaches its forward position and is in standstill, the pressure in conduit |02 will greatly increase so as to overcome the pressure of spring 85 and to move the locking members 13 and 14 into engagment with cylinder 51, rmly locking the same in its forward operative position.

The line pressure is maintained during turning operation.

When, after turning, it is desired to move the work piece, the following procedure is followed:

While the pressure is maintained in conduit 53, the valve |88 is turned so as to connect the conduit |02 with an outlet conduit leading to tank |04 and to simultaneously connect port 85 with a pressure conduit including the pump |83. Thereby hydraulic pressure yfluid is forced into the space 91 behind the stationary piston 92, moving the cylinder 5'I together with quill 0I and center 65 against direction of arrow IEII. During this movement, disengagement of the tailstock center- 65 from the work piece I I is prevented by the fact that the work piece will be forced by the Y tracted position, valve 89 is automatically operi ated, e. g.l by a pre-set electric switch which actuates asolenoid shifting valve 99, soastoconretracting the headstock .center 4I and moving it out of engagement withl the corresponding center hole of the work piece, thus safely depositing this work piece on the lifting means moved in the meantime under the work piece.

The subject matter of the present application is partly disclosed in the U. S. patent application Serial No..131,2'73, filed by Robert Kurzweil on June 5, 1948, for a Hydraulically Operated Headstock Center.

It will be understood that each of the. elements described above, or two or more together, may also nd a useful application in other types of metal working machines differing from the types described above.

While we have illustrated and described the invention as embodied in lathes for turning heavy work pieces, we do not intend to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of this invention.

Without further analysis, the foregoing will so fully reveal the gist of our invention that others can by applying currentknowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention, and, therefore, Vsuch adaptations should and are intended to be ccmprehended within the meaning and range of equivalence of the following claims.

What we claim as new and desire to secure by Letters Patent is:

1. In a lathe tailstock equipped with ,a tailstock body, a quill arangement mounted Iwithin said tailstock body rotatably and slidably in axial direction thereof, a tailstock center mounted within said quill arrangement slidably in axial direction of said tailstock body relative to said quill arrangement, resilient means permanently forcing said tailstock center outward into operative position adapted to engage one end of a work piece, .and gripping means on said quill arrangement for grippingly engaging said end of said work piece around said tailstock center, the cornbination of first hydraulic operating means for sliding said quill arrangement together with said tailstock center and said gripping means forward into operative position in which said tailstock center and said gripping means engage said end of said work piece and backward into inoperative position with said tailstock center and said gripping means not engaging said end of said work piece; locking means for holding said quill arrangement in operative position; second hydraulic operating means for moving said locking means into operative locking position; and combined hydraulic actuating means for rst actuating said rst hydraulic operating means and then automatically actuating said second hydraulic operating means and thereby moving said locking means into operative locking position after said rst hy.- draulic operating means have slid said quill arrangement together withsaid tailstock center and said gripping means forward into operative position.

2. In a lathe tailstock equipped with a tailstock body, a quill arrangement mounted Awithin said tailstock body rotatably and slidably in axial direction thereof, a tailstock center mounted within said quill arrangement slidably in axial direction -of said tailstock bodyV relative tosaid` quill arrangement, resilient means permanently forcing said tailstock center outward into operative position adapted to engage one end of a work piece, and gripping means on said quill arrangement for grippingly engaging said end of said work piece around said tailstock center,v in combination, first hydraulic operating means for sliding saidquill arrangement together with said tailstock center and said gripping means forward into operative position in which said tailstock center and said gripping means engage said end of said work piece and backward into inoperative position with said tailstock center and said gripping means not engaging said end of said work piece; locking means for holding said quill arrangementI in operative position; second hydraulic operating means for moving said locking means into operative locking position; and spring means for moving said locking means into inoperative non-locking position when said second hydraulic operating means are not holding said locking means in operative position.

3. In a lathe tailstock equipped with a tailstock body, a quill arrangement mounted within said tailstock body rotatably and slidably in axial direction thereof, a tailstock center mounted within said quill arrangement slidably in axial direction of said tailstock body relative to said quill arrangement, resilient means permanently forcing said tailstock center outward into operative position adapted to engage one end of a work piece, and gripping means on said quill arrangement for grippingly engaging said end of said work piece around said tailstock center, in combination first hydraulic operating means for sliding said quill arrangement together with said tailstock center and said gripping means forward into operative position in which said tailstock center and said gripping means engage said end of said work piece and backward into inoperative position with said tailstock center and said gripping means not engaging said end of said work piece; locking means for holding said quill arrangement in operative position; second hydraulic operating means for moving said locking means into operative locking position; spring means for moving said Vlocking means into inoperative non-locking position when said second hydraulic operating means are not holding said locking means in operative position; and combined hydraulic actuating means for first actuating said first hydraulic operating means and then automatically actuating Vsaid second hydraulic operating means and thereby moving said locking means into operative locking position after said first hydraulic operating means have slid said quill arrangement together with said tailstock center and said gripping means forward into operative position.

4. In a lathe tailstock equipped with a tailstock body, a cylindrical support mounted within said tailstock body non-rotatably but slidably in axial direction thereof, a quill mounted within said cylindrical support at the front end thereof rotatably relative to said cylindrical support, but non-slidably in axial direction thereof, a tailstock center mounted within said quill slidably in axial direction thereof, resilient means permanently forcing said tailstock center outward into operative position adapted to engage one end of a work piece, and gripping means on the front end of said quill for grippingly engaging said end of said work piece around said tailstock center when said cylindrical support is moved within said tailstock body forward into operative position, in combination, a cylindrical bore within the rear' part of said cylindrical support extending in axial direction thereof; a stationary piston within said cylindrical bore forming within the same a forward and a rearward cylinder compartment; a cover secured to the rear face of said cylindrical support closing said cylindrical bore within the same; an aperture within said cover; a stationary piston rod passing through said aperture and secured at its front end to said stationary piston and at its rear end to said tailstock body extending in axial direction of said cylindrical support; a first hydraulic conduit passing through said stationary piston rod and leading into said forward compartment within said bore; a second hydraulic conduit passing through said stationary piston rod and leading into said rearward compartment within said A cylindrical bore; combined valve means connected to said hydraulic conduits so as to be adapted tol connect each of the same either with a source of pressure fluid or an exhaust conduit for said fluid; locking means for holding said cylindrical support in operative position; hydraulic operating means for moving said locking means into operative locking position and holding said locking means in such operative position; and a third hydraulic conuit connecting said first hydraulic conduit with said hydraulic operating means and serving for moving said locking means,

5. In a lathe tailstock equipped with a tailstock body; a cylindrical support mounted Within said tailstocl: body non-rotatably but slidably in axial direction thereof, a quill mounted within said cylindrical support at the front end thereof rotatably relative to said cylindrical support, but non-slidably in axial direction thereof, a tailstock center mounted within said quill slidably in axial direction thereof, resilient means permanently forcing said tailstock center outward into operative position adapted to engage one end of a work piece, and gripping means on the front end of said quill for grippingly engaging said end of said work piece around said tailstcck center when said cylindrical support is moved within said tailstock body forward into operative position, in combination, a cylindrical bore within the rear part of said cylindrical support extending in axial direction thereof; a Stationary piston within said cylindrical bore forming within the same a forward and a rearward cylinder compartment; a cover secured to the rear face of said cylindrical support closing said cylindrical bore within the same; an aperture within said cover; a stationary piston rod passing through said aperture and secured at its front end to said stationary piston and at its rear end to said tailstock body extending in axial direction of said cylindrical support; a first hydraulic conduit passing through said stationary piston rod and leading into said forward compartment within said bore; a second hydraulic conduit passing through said stationary piston rod and leading into said rearward compartment within said cylindrical bore; combined valve means ccnnected to said hydraulic conduits so as to be adapted to connect each of the same either with a source of pressure uid or an exhaust conduit for said fluid; locking means for holding said cylindrical support in operative position;v hydraulicv operating means for moving said locking means into operative locking position and holding said locking means in such operative position; a third hydraulic conduit connecting said first hydraulic conduit with said hydraulic operating means and serving for moving said locking means; and spring means for moving said locking means Vinto inoperative non-locking position when said hydraulic operating means are not operated by pressure fluid admitted through said third fluid conduit and are therefore, not moving said locking means into operative position and holding it in such position.

6. In a lathe tailstock in combination, a quill arrangement mounted within said tailstock slidably in axial direction; first hydraulic operating means for sliding said quill arrangement forward into operative position and backward into inoperative position; locking means for holding said quill arrangement in operative position; second hydraulic operating means for moving said locking means into operative locking position; and combined hydraulic actuating means for first actuating said first hydraulic operating means and thereby moving said locking means into operative locking position after said first hydraulic operating means have slid said quill arrangement forward into operative position.

7. In a lathe tailstock in combination, a quill arrangement mounted within said tailstock slidably in axial direction; first hydraulic operating means for sliding said quill arrangement forward into operative position and backward into inoperative position; locking means for holding said quill arrangement in operative position; second hydraulic operating means for moving said locking means into operative locking position; and spring means for moving said locking means into inoperative non-locking position when said second hydraulic operating means are not holding said locking means in operative position.

8. In a lathe tailstock in combination, a quill arrangement mounted within said tailstock slidably in axial direction; rst hydraulic operating means for sliding said quill arrangement forwardr into operative position and backward into inoperative position; locking means for holding said quill arrangement in operative position; second hydraulic operating means for moving said locking means into operative locking position; spring means for moving said locking means into inoperative non-locking position when said second hydraulic operating means are not holding said locking means in operative position; and combined hydraulic actuating means for rst actuating said rst hydraulic operating means and then automatically actuating said second hydraulic operating means and thereby moving said locking means into operative locking position after said rst hydraulic operating means have slid said quill arrangement into operative position.

9. In a lathe tailstock a tailstock body; a cylindrical support for a tailstock center mounted within said tailstock slidably in axial direction thereof; a cylindrical bore within the rear part of said cylindrical support extending in axial direction thereof; a stationary piston within said cylindrical bore forming within the same a forward and a rearward cylinder compartment; a cover secured to the rear face of said cylindrical support closing said cylindrical bore within the same; an aperture within said cover; a stationary piston rod passing through said aperture and secured at its front end to said stationary piston and at its rear end to said tailstock body extending in axial direction of said cylindrical support; a rst hydraulic conduit passing through said stationary piston rod and leading into said forward compartment within said bore; a second hydraulic conduit passing through said stationary piston rod and leading into said rearward compartment within said cylindrical bore; combined valve means connected to said hydraulic conduits so as to be adapted to connect each of the same either with a source of pressure fluid or an exhaust conduit for said fluid; locking means for holding said cylindrical support in operative position; hydraulic operating means for moving said locking means into operative locking position and holding said locking means in such operative position; and a third hydraulic conduit connecting said first hydraulic conduit with said hydraulic operating means and serving for moving said locking means.

10. In a lathe tailstock a tailstock body; a cylindrical support for a tailstock center mounted within said tailstock slidably in axial direction thereof; a cylindrical bore within the rear part of said cylindrical support extending in axial direction thereof; a stationary piston within said cylindrical bore forming within the same a forward and a rearward cylinder compartment; a cover secured to the rear face of said cylindrical support closing said cylindrical bore within the same; an aperture within said cover; a stationary piston rod passing through said aperture and secured at its front end to said stationary piston and at its rear end to said tailstock body extending in axial direction of said cylindrical support; a rst hydraulic conduit .passing through said stationary piston rod and leading into said forward compartment within said bore; a second hydraulic conduit passing through said stationary piston rod and leading into said rearward compartment within said cylindrical bore; combined valve means connected to said hydraulic conduits so as to be adapted to connect each of the same either with a source of pressure uid or an exhaust conduit for said fluid; locking means for holding said cylindrical support in operative position; hydraulic operating means for moving said locking means into operative locking position and holding said locking means in such operative position; a third hydraulic conduit connecting said first hydraulic conduit with said hydraulic operating means and serving for moving said locking means; and` spring means for moving said locking means into inoperative non-locking position when said hydraulic operating means are not operated by pressure fluid admitted through said third fluid conduit and` are therefore, not moving said locking means into operative position and holding it in such position.

ROBERT KURZWEIL. JUVENTINO J. PESQUEIRA.

REFERENCES CITED The following references are of record in the file of this patent: f

UNITED STATES PATENTS Number Name Date 1,361,120 Weatherby Dec. 7, 1920 1,934,975 Groene Nov. 14, 1933 1,970,023 Schroeder Aug. 14, 1934 2,211,722 Groene Aug. 13, 1940 2,257,452 Binns Sept. 30, 1941 2,372,692 Svenson Apr. 3, 1945 2,396,399 Veale Mar. 12, 1946 FOREIGN PATENTS Number Country Date 462,847 Great Britain Mar. 17, 1937 

